WPF 设置窗口数据上下文

Question

我是一个WPF的初学者，请多包涵。我有一个简单的应用程序，可以将华氏度转换为摄氏度，反之亦然。我想尝试重构这个应用程序，使用MVVM模式，所以我将所有东西从我的代码后台移动到了一个单独的类中，然后以编程方式设置了数据上下文。但是我得到了很多“在上下文中不存在”的错误。我做错了什么？谢谢

XAML

<Window x:Class="FarenheitCelciusConverter.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Temperature Converter" Height="500" Width="500"
xmlns:local="clr-namespace:FarenheitCelciusConverter">
<Grid HorizontalAlignment="Left" VerticalAlignment="Top" Height="473" Width="488">

    <Label Height="28" HorizontalAlignment="Left" Margin="10,10,0,0" Name="lblF" VerticalAlignment="Top" Width="64" FontWeight="Bold">Farenheit</Label>
    <Label Height="28" HorizontalAlignment="Left" Margin="10,42,0,0" Name="lblC" VerticalAlignment="Top" Width="64" FontWeight="Bold">Celcius</Label>
    <TextBox Height="23" Margin="94,10,112,0" Name="tbFaren" VerticalAlignment="Top" Width="72" HorizontalAlignment="Left" />
    <TextBox Height="23" Margin="94,42,112,0" Name="tbCelcius" VerticalAlignment="Top" Width="72" HorizontalAlignment="Left" />
    <Button Margin="94,76,109,0" Name="btnConvert" Click="btnConvert_Click" Height="23" VerticalAlignment="Top" HorizontalContentAlignment="Center" Width="72" HorizontalAlignment="Left">Convert</Button>
    <Image Name="image1" Stretch="Fill" Margin="94,112,240,228">
        <Image.Source>
            <BitmapImage DecodePixelWidth="200" UriSource="C:\Users\Winston\Pictures\thermometer.jpg"/>
        </Image.Source>
    </Image>
    <TextBlock FontWeight="Bold" Height="21" Margin="195,12,173,0" Name="tblCelci" VerticalAlignment="Top" /><TextBlock FontWeight="Bold" Height="21" Margin="195,44,0,0" Name="tblFarenh" VerticalAlignment="Top" HorizontalAlignment="Left" Width="120" /><TextBlock FontWeight="Bold" Height="21" Margin="195,78,15,0" Name="tblCex" VerticalAlignment="Top" Foreground="Red" />
</Grid>
</Window>

代码后台

namespace FarenheitCelciusConverter
{
/// <summary>
/// Interaction logic for Window1.xaml
/// </summary>
public partial class Window1 : Window
{
    public Window1()
    {
        InitializeComponent();
        DataContext = new ConverterViewModel();
    }   
}

}

View Model

namespace FarenheitCelciusConverter
{
    public class ConverterViewModel
    {        
    private void btnConvert_Click(object sender, RoutedEventArgs e)
    {
        tblCex.Text = "";

        try
        {
            if (tbCelcius.Text.Length != 0)
            {
                double celcius = Double.Parse(tbCelcius.Text);

                if (celcius < 99999.0 && celcius > -99999.0)
                {
                    tblFarenh.Text = Math.Round(1.8 * celcius + 32.0) + " F";
                }
                else
                {
                    throw new OverflowException("Number limit exceeded!");
                }
            }

            if (tbFaren.Text.Length != 0)
            {
                double farenh = Double.Parse(tbFaren.Text);

                if (farenh < 99999.0 && farenh > -99999.0)
                {
                    tblCelci.Text = Math.Round(0.555 * (farenh - 32.0)) + " C";
                }
                else
                {
                    throw new OverflowException("Number limit exceeded!");
                }
            }
        }

        catch (Exception ex)
        {
            tblCex.Text = ex.Message;
        }

    }  
}

}

- OO_Learner

Answer 1

当使用MVVM模式时，数据通过数据绑定从视图（Window1）传递到ViewModel，然后再传递回来。因此，您的每个文本框都应该与ViewModel中的公共属性进行数据绑定：

<TextBox Height="23" Margin="94,10,112,0" Name="tbFaren" VerticalAlignment="Top" Width="72" HorizontalAlignment="Left" Text="{Binding FahrenText}"/>

您的ViewModel将获取属性中的值，对其进行一些操作，并将属性与相应的文本框绑定。这样，ViewModel执行逻辑，View根据您给出的规则解释输出。稍后，您可以更改View中的规则，而不会影响ViewModel，而使用codebehind，则必须在程序逻辑旁边明确设置View设置。

此外，请务必在ViewModel上实现iNotifyPropertyChanged接口，否则UI将不知道数据绑定属性值何时更改，也不会更新。请查看此文章 示例。 同时，这是WPF数据绑定的MSDN文章。。

- CodeWarrior